Anthracycline antineoplastics include doxorubicin (sold under the trademark ADRIAMYCIN, NSC 123127, from Adria Laboratories, Columbus, Ohio), an antibiotic isolated from the culture of a mutant Streptomyces peucetius strain. Other anthracyclines include: daunorubicin (sold under the trademark CERUBIDINE, from Wyeth Laboratories, Philadelphia, Pa.) epirubicin (4' epi-doxorubicin), THP-Adriamycin, and idarubicin (4' deoxy-doxorubicin).
Doxorubicin is effective as an anti-tumor agent against a variety of neoplasms. It is believed that doxorubicin's anti-tumor effects are due to DNA inhibition by intercalation between base pairs and/or steric inhibition of RNA activity.
Doxorubicin is effective in treatment of acute leukemias and malignant lymphomas. It is also very effective in the treatment of solid tumors, particularly when administered as part of a combination regimen. Thus, when used with cyclophosphamide, vincristine, bleomycin, and prednisone (BACOP), non-Hodgkin's lymphomas can be treated. Hodgkin's disease can be treated using a regimen of doxorubicin with bleomycin, vinblastine, and dacarbazine (ABVD). Carcinoma of the ovary is treated with a combination of cyclophosphamide, doxorubicin and cisplatin. Doxorubicin is effective against a number of sarcomas, e.g., osteogenic, Ewings's and soft-tissue sarcomas, and is considered the drug of choice, alone or in combination with other chemotherapeutic agents, in the treatment of metastatic adenocarcinoma of the breast, carcinoma of the bladder, bronchogenic carcinoma, neuroblastoma, and metastatic thyroid carcinoma. Doxorubicin has also shown activity in the treatment of carcinomas of the endometrium, testes, prostate, cerviy, head and neck, and plasma-cell myeloma. Another widely used combination chemotherapy involves the use of doxorubicin, cyclophosphamide, and fluorouracil (FDC). FDC is used most commonly for the treatment of metastatic carcinoma of the breast.
The chief acute toxic effect of doxorubicin is myelosuppression. The peak of myelosuppression usually occurs at approximately 14.+-.2 days, with recovery occurring at 15-18 days. Alopecia (hair loss) occurs frequently and begins in the third or fourth week of treatment. Nausea and vomiting occur regularly. Patients typically receive doxorubicin in dosages of 50-75 mg/m.sup.2 (milligrams per square meter of body surface) per 21 day cycle.
Another important toxic effect of doxorubicin, and other anthracyclines, is cardiotoxicity. Patients who have received accumulated doxorubicin doses greater than 450 mg/m.sup.2 are considered at high risk (greater than 10%) for the development cardiotoxicity, such as clinical heart failure. Cardiotoxicity is the major limitation in the usefulness of doxorubicin. In addition to clinical heart failure, cardiotoxicity encompasses clinical cardiotoxicity such as congestive heart failure and/or cardiac arrhythmias, and subclinical cardiotoxicity such as that detected by pathologic changes in cardiac biopsy or decrease in ventricular ejection fractions. Thus, it has been found that doxorubicin treatment often must be terminated before the maximum effective cumulative dose has been administered to a patient bearing a neoplasm, because of the development of life-threatening cardiomyopathy. Cardiotoxicity is manifested by chronic congestive heart failure, unresponsive to digitalis. At cumulative dosages of 300 mg/m.sup.2 it has been demonstrated that about 50% of women with breast cancer develop a fall in the left ventricular ejection fraction (LVEF), measured by multigated radionuclide angiographic (MUGA) scan. Thus, although doxorubicin is considered a highly effective anti-tumor agent, this effectiveness is mitigated by the concomitant cardiotoxicity encountered with use of the drug.
The mechanism for doxorubicin (and other anthracycline) -induced cardiotoxicity is not completely understood, but is believed to involve drug-induced, cytotoxic, free-radical formation. These free radicals are formed via a cytochrome P450 reductase-mediated reaction and the formation of a semiquinone radical intermediate. As a result, damage occurs to mitochondrial membranes, endoplasmic reticulum, and nucleic acids. The heart muscle is particularly susceptible to free-radical damage because it has less protective superoxide dismutase and catalase activity than other tissues. Further, doxorubicin directly depresses cardiac glutathione peroxidase activity, the major defense against free-radical damage.
It has been found that doxorubicin binds with iron with high affinity. In vitro, the iron-doxorubicin complex causes oxygen radical formation and marked lipid peroxidation. The iron-doxorubicin complex has also been determined to cause increased oxygen radical production over doxorubicin alone.
If the cardiotoxicity associated with doxorubicin could be overcome, this drug, administered alone or in combination with other chemotherapeutic agents, would be the treatment of choice in many situations. For example, administration of doxorubicin is typically terminated when the total cumulative dose attains 450 mg/m.sup.2, because it has been found that at this dosage approximately 5-10% of patients develop unacceptable clinical toxicity. In addition, many patients already receiving doxorubicin at this maximum dosage could derive substantial benefit from even higher dosages. However, increased dosages have been precluded by the increased risk of cardiotoxicity. The risk increases sharply with increasing cumulative dosages above 450 mg/m.sup.2. For an even greater number of patients where doxorubicin would otherwise be part of the treatment of choice, the drug must be withheld completely because of high cardiac risk factors, e.g., age, chest-wall radiation from previous cancer treatment, or cardiac disease. This is particularly true when adjuvant ("preventive") chemotherapy is considered. For example, doxorubicin is sometimes used in an adjuvant setting. Patients with breast cancer are often treated by surgery for removal of the primary tumor sometimes followed by radiation therapy. In this situation, it is common to administer adjuvant chemotherapy following treatment of the primary tumor to prevent recurrence. Here, the risk of cardiotoxicity may outweigh the possible benefit of such preventive therapy. Adjuvant doxorubicin is also used in treatment of sarcomas, lymphomas, and leukaemia. In these cases, the risk of cardiotoxicity in otherwise apparently healthy patients (i.e., no longer suffering from primary tumor) may be too great to justify adjuvant chemotherapy with doxorubicin.
To reduce the occurrence of cardiotoxicity associated with doxorubicin administration, three strategies have been pursued. One method is to alter the dosing schedule of the drug. It is believed that the cardiotoxic effects of anthracyclines are related at least in part to peak blood levels of the drug, while anti-tumor activity is related to total drug exposure. Partial success in reducing cardiotoxicity while maintaining tumoricidal effects has been achieved by administering e.g., doxorubicin by infusion over extended periods, e.g., 96 hours. Although this method has produced a small but measurable decrease in cardiotoxicity, it requires patients to wear portable, but inconvenient, infusion devices, or indwelling catheters and pumps are necessary for prolonged infusions, causing long and expensive hospitalization. Altogether, infusion over extended periods is difficult in an out-patient setting.
A second approach to the reduction of cardiotoxicity of anthracyclines was an effort to develop anthracycline analogues having the anti-tumor activity of e.g., doxorubicin, without the cardiotoxicity. To date, no such analogues have been found which clearly meet these criteria.
A third strategy, the subject of this patent application, is the mitigation of anthracycline cardiotoxicity using cardioprotective agents. This approach is attractive because it allows well-established administration schedules of anthracyclines to be maintained without resort to prolonged infusions. This strategy presumes that separate mechanisms are responsible for tumoricidal and cardiotoxic effects of anthracyclines.
Studies have been conducted with several agents believed to be cardioprotective agents. Alpha-tocopherol and N-acetyl cysteine have been evaluated as cardioprotective agents only partially in mice, but studies in humans and other species, did not result in significant cardioprotection against doxorubicin-induced toxicity. Two agents which have shown promise as doxorubicin cardioprotectors in studies performed with non-cancer-bearing animals, are ICRF 159 and ICRF 187.
ICRF 159 (NSC 129943) and ICRF 187 (NSC 159780) are chelating agents of the bis(dioxopiperazine) family, chemically resemble ethylenediaminetetraacetic acid (EDTA), and have the formula (.+-.)-(1,2-bis(3,5-dioxopiperazinyl-1-yl)propane. ICRF (Imperial Cancer Research Fund) 187 is the (+) enantiomer of ICRF 159 and is more water soluble. Thus, ICRF 187 is the preferred isomer for the preparation of parenteral injections.
ICRF 159 and 187 were initially investigated for anti-tumor activity. Unfortunately, both compounds were found to have little effect against human tumors when administered as single agents. Although the mechanism of action of bis(dioxopiperazine)s in reducing anthracycline cardiotoxicity is unknown, these compounds chemically resemble EDTA, and have potent chelating activity. ICRF 187 has been reported to form a bidentate chelator by intracellular hydrolysis. It has also been reported that EDTA can prevent erythrocyte ghost destruction by the iron-doxorubicin complex, possibly by chelating with bivalent iron. Thus it is believed by the present inventors, though it has not been demonstrated, that the chelating agent competes with doxorubicin for intracellular iron (and therefore prevents free radical formation), or that it may act as a free radical scavenger within the cardiac cell.
Several animal studies have been conducted to assess the cardioprotective effect of ICRF 187 when used in conjunction with an anthracycline. For example, an article by Herman, E. H. et al, in Cancer Treat. Rep. 63: 89-92, 1979, reported that a reduction of lethality and cardiotoxicity associated with administration of the anthracycline daunorubicin, was obtained by prior administration of ICRF 187 in non-cancer-bearing Syrian golden hamsters.
In 1981, Herman, E. H. et al, reported in Res. Com. Chem. Path. Pharm. 31: 85-97, that chronic daunorubicin cardiotoxicity was reduced by ICRF 187 administration in non-cancer-bearing rabbits. The ICRF 187 was administered 30 minutes prior to the daunorubicin at doses of 12.5 and 25 mg/kg (milligrams per kilogram of body weight).
An article published in Cancer Res. 41 3436-3440, 1981, by Herman, E. H. et al, showed a reduction in chronic cardiotoxicity induced by Adriamycin in normal (non-cancer-bearing) beagle dogs if administration of Adriamycin was preceded by administration of ICRF 187. In this randomized study, ICRF 187 administered at 12.5 mg/kg 30 minutes prior to injection with Adriamycin at 1.0 mg/kg, prevented cardiotoxicity in all treated animals.
Herman, E. H et al published a report in Lab. Invest. 49: 69-77, 1983, that doxorubicin treatment lead to myocardial lesions in eight of nine non-cancer-bearing miniature swine. However, cardiac lesions were absent in two, and minimal in five of the seven animals given doxorubicin (at 14.4 mg/kg) in combination with ICRF 187.
In another beagle study, Herman, E. H. et al reported, at Cancer Res. 45: 276-281, 1985, that no abnormalities were found in the hearts of three of six non-cancer-bearing dogs administered doxorubicin and ICRF 187, and that the remaining three dogs had minimal heart lesions.
In one human study of the toxic effect of ICRF 187 administered as an antitumor agent, it was found that dose limiting toxicity occurs at 1500 mg/m.sup.2 administered three times daily, every three days, in patients with cancer. For this study, ICRF 187 was the only chemotherapeutic agent administered. At this dosage level the predominant adverse effects were leukopenia and thrombocytopenia. The cardio-toxic effects at this dosage included mild elevations of SGOT (serum glutamate-oxalate transaminase) and SGPT (serum glutamic-pyruvic transaminase), occasional vomiting and some alopecia (hair loss) (See, Von Hoff, D. D. et al, Cancer Treat. Rep. 65: 249-252, 1981).